For high capacity installations, as may be incorporated in office and apartment blocks, a refrigeration system of high output is necessary to be able to handle the maximum load expected. In practice, such high output refrigeration systems tend to be more prone to breakdown and failure than do lower output refrigeration units. Such breakdowns and failures often leave the building in which the system is installed without any air conditioning until the breakdown or failure is remedied. In high capacity systems, breakdowns and failures can often take days and, sometimes, weeks to repair.
Further, in the design and construction of many modern building structures, provision is made for the expansion of the building structure, that is, the building is constructed in a number of stages spread over a period of time. Because of the difficulty in expanding a predesigned air conditioning system, it is generally necessary to design and install the system to have the air conditioning capacity for the completed building structure. This means, therefore, that the system is running, inefficiently, at less than full load capacity until such time as all building stages are completed.
In other instances, building structures are extended after the initial design and construction, and such extensions often require the air conditioning system for the initial building structure to be completely replaced with a new system to be able to handle the load of the extended building structure.